Goodrive30 Series VFD Communication protocol
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In the ladder logic, CKSM uses the table look-up method to calculate the CRC value according
to the content in the frame. The program of this method is simple, and the calculation is fast,
but the ROM space occupied is large. Use this program with caution in scenarios where there
are space occupation requirements on programs.
7.3 RTU command code and communication data
7.3.1 Command code 03H, reading N words (continuously up to 16 words)
The command code 03H is used by the master to read data from the VFD. The count of data
to be read depends on the "data number" in the command. A maximum of 16 pieces of data
can be read. The addresses of the read parameters must be contiguous. Each piece of data
occupies 2 bytes, that is, one word. The command format is presented using the hexadecimal
system (a number followed by "H" indicates a hexadecimal value). One hexadecimal value
occupies one byte.
The command code is used to read the working status of the VFD.
For example, starting from the data address of 0004H, to read two contiguous pieces of data
(that is, to read content from the data addresses 0004H and 0005H) of the VFD whose slave
address is 01H, the frame structures are described in the following.
RTU master command (sent from the
master to the VFD)
RTU slave response (sent from the VFD to
the master)
Start address
high-order bit
High-order bit of data
in 0004H
Start address
low-order bit
Low-order bit of data
in 0004H
Data number
high-order bit
High-order bit of data
in 0005H
Data number
low-order bit
Low-order bit of data
in 0005H
"START" and "END" are "T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)", indicating
that a time gap with a mini. length of 3.5 bytes must be kept before RS485 communication is
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